The present invention relates to a method and system for detecting a defect or failure of a compressed air load circuit in an electronic compressed air system for vehicles.
Conventional multi-circuit protective valves divide energy supply into several mutually independent load circuits and, in the event of failure of one load circuit, for example by line rupture, maintain a minimum pressure in the intact circuits. If a defect allowing more air to be lost than can be resupplied by the compressor occurs in a service-brake circuit, the pressure in the service-brake circuit drops until the pressure reaches the closing pressure of the valve. The pressure in the defective circuit continues to drop, whereas the closing pressure is maintained in the intact circuit. While the pressure in the defective circuit continues to drop, the circuit that is still intact can be refilled by the compressor until the opening pressure of the defective circuit is reached. There is established a dynamic equilibrium, in which the delivered compressed air can supply the circuits that are still intact (as well as secondary load circuits), although at the same time air is being lost via the defect. A disadvantage of conventional multi-circuit protective valves is that the maximum pressure in the brake system is equal to the opening pressure of the defective circuit when it breaks. Another disadvantage is that the pressure momentarily drops to the closing pressure of the defective circuit. Yet another disadvantage in particular is the relatively large energy loss in the event of a circuit failure, because defective circuits are detected and shut off at a relatively late stage.